Oscillation generating system



Feb. 1944. w KQCK 2,342,286

OSCILLATION GENERATING SYSTEM Filed Oct. 1, 1941 2 Sheets-Sheet lINVENTCR Q WINSTON E. KOCK W7 ATTORNEY Feb. 22, 1944. w. E. KOCKOSCILLATION GENERATING SYSTEM 1, 1941 2 Sheets-Sheet 2 Filed'Oct.

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.INVENTOR WINSTON E. KOCK ATTORNEY Patented Feb. 22, 1944 UNITED STATESRATENT OFFICE OSCILLATION GENERATING SYSTEM Winston E. Kock, Cincinnati,Ohio, assignor to The Baldwin Company, Cincinnati, Ohio, a corporationof Ohio 6 Claims.

My invention relates to the production of electric oscillations. It isparticularly useful in the electrical production of music, andaccordingly will be set forth in the present disclosure in the form ofan assembly for generating audio frequency oscillations for the variousnotes and tone color systems of a polyphonic electrical musicalinstrument.

As a general object the invention contemplates an oscillation generatingassembly having the fundamental advantages of low cost of construction,stability and durability, in which oscillations are generated accordingto tone color re quirements set forth in my United States Patent No.2,233,948 issued March 4, 1941, for improvements in Electrical organs.That is, it is an object of the invention to provide an economicaloscillation generating assembly in which oscillation waveforms arecomplex, i. e., have considerable harmonic content, and are essentiallysimilar for the various oscillation frequencies of the instrument,octavely assigned oscillations are maintained in exact octaverelationship, and octavely related oscillations as derived from theassembly are substantially in phase.

Briefly, I accomplish theabove by providing a plurality of cascades ofelectric oscillation generators known as phase-shift oscillators,onesuch cascade being provided for each of the series of octavelyrelated notes in a multioctave musical instrument. At the head of eachcascade I provide a suitable stabilized or master oscillator having thefrequency of the top note cf'the corresponding octave series. Thismaster generator in turn controls a phase-shift oscillator suitablyarranged so that the latter operates under the control at an exactoctave below the master, thereby corresponding to the second note of theseries; the oscillator thus controlled then controls a secondphase-shift oscillator so that the second controlled oscillator operatesexactly an octave below the first, corresponding to the third note ofthe series; and so on throughout the series, as many members beingprovided for the various cascades as necessary toattain the desired notecompass of the instrument.

With reference to the term phase-shift oscillator the type ofoscillation generator I employ may be thought of in principle as asingle stage vacuum tube resistance-coupled amplifier having its outputcircuit coupled to its input circuit through a suitable phase shiftingnetwork, so that the device becomes a self-oscillator of theregenerative type (as distinguished from arelaxation. oscillator) It isknown that the grid input and plate circuit output voltages of a singletube resistance-coupled amplifier are normally out-of-phase, and asimple coupling of the two circuits will therefore not produceregenerative action. If, however, a network effecting a phase change ofthe order of for oscillations passing through it is employed for thecoupling, regenerative action is obtained and the device hecomes theoscillator indicated, providing the tube has suiiicient voltage gain toovercome the attenuation in the network. It happens that suitable tubesfor the purpose are readily available among the tubes now employed inradio receivers and I shall later indicate a particular type of tube Iprefer to employ.

As to the phase shifting network I use a type of network comprisingcapacities in a series arrangement shunted by resistances. This has theadvantage that the parts employed are relatively low in cost. Atfrequencies above the designed frequency of the oscillator thereactances of the capacities (which produce the phase shift) becomenegligible as compared with the resistances so that phase shaft does nottake place, whereas at frequencies below the designed frequency theexcessive reactances of the capacities result in either too much phaseshift to produce oscillation and/or the capacity reactances produce toomuch voltage attenuation for sustained oscillation to result.Consequently the device oscillates at a definite frequency or within asmall range of frequencies. (I shall later show that a particularmodification of a phase-oscillator can be provided having suificientfrequency stability so that it is suitable as a master oscillator in anelectrical musical instrument.)

I have found in employing phase-shift oscillators in cascades such asdescribed below that they are particularly susceptible of being raisedin frequency under the influence of periodic electric pulses of higherfrequency, so that under the control of the pulses they operate at anexact subharmcnic of the pulse frequency. In the instance of a musicalinstrument the suboctave is an especially desired subharmonic and underthis condition I have found it advantageous to set a phase-shiftoscillator about six semitones below the frequency to which it is to beraised by control. For example, if the oscillator is to operate at the Cnote of 1046.5 C. P; S; (cycles per second) under the control ofpulsesffrom the C noteat 2093 C. P. S. the oscillator should oscillateunattended at about 740 C. P. S. (about Ft' 'below the 1046.5 C). Thisparticular feature has been previously discussed in the aforementionedPatent No. 2,233,948 and in United States Patent No. 2,230,429 issuedFebruary 4, 1941, to John F. Jordan and myself as joint patentees forMeans for generating electric oscillations.

I have furthermore found that under suitable arrangement phase-shiftoscillators can be made incapable of sustained oscillations but thatunder this suitable non-oscillatory condition will operate verysatisfactorily as frequency dividers when pulsed as aforesaid, just aswhen they are selfoscillatory. The same relations, as to frequencyraising and the like as discussed just above, hold for thisnon-oscillatory condition. The use of the devices asnon-self-oscillatory frequency dividers is especially advantageous inthe electrical production of music, since the failure of a device 1results only in silence from the notes corresponding to the elementsbelow it in a cascade series, rather than the production of off-pitchtones. The advantage of this has been previously recognized, in theaforementioned Patent No. 2,230,429 and in United States Patent No.2,185,635 issued January 2, 1940, to John F. Jordan and myself as jointpatentees for Frequency dividers,

As to a further use for non-oscillatory phaseshift devices I have alsofound that they may be advantageously employed in the tone colorcircuits of electrical musical instruments, as filters for accentuatingand/or attenuating the harmonics of complex oscillations withinpredetermined frequency bands to form particular tone colors.

A detailed manner in which the above is attained and the attainment ofthose further objects of the invention which will be indicatedhereinafter or will occur to those skilled in the art on reading thisspecification, will now be described specifically, reference being madeto the accompanying drawings forming a part hereof, wherein:

Figure 1 is a wiring diagram of a master oscillation generator and acascade of oscillation generating devices for producing octavely relatedoscillations;

Figure 2 illustrates the waveform of pulses such as are used forfrequency control in the cascade of Figure 1;

Figure 3 represents the waveform of oscillations generated by a devicesuch as those in the cascade of Figure 1, when not operated upon bycontrolling pulses; whereas Figure 4 illustrates the waveform ofoscillations derived from such a device when acted upon by controllingpulses;

Figure 5 is a wiring diagram of a modified form of oscillationgenerating device;

Figure 6 illustrates the use of devices such as that of Figure 5 as amaster oscillation generator and as an associated frequency divider; and

Figure '7 illustrates the use of a device such as that of Figure 5 as ameans for modifying oscillations for tone color purposes.

Throughout the various figures of the drawings I have illustrated groundby the conventional symbol, and unless otherwise set forth in thisdescription ground will be used as a return for circuits and as a commonor reference potential. Thus for example the sources of direct currentpotential +13 and V indicated in the drawings are referred to ground fortheir return terminals. These sources +3 and V may of course be obtainedby suitable ectification and filtering of commercial alternatingcurrent.

With detailed reference to Figure 1, I have shown a cascade ofphase-shift devices as above outlined, for the C notes of an electricalmusical instrument, it being understood that a corresponding cascade,except for values of parts, is provided for each of the remaining groupsof octavely related notes in the instrument. As illustrated the devicesof Figure 1 contain respective vacuum tubes T, each tube having an anodeA, a thermionic cathode K, and a control grid G between these twoelements. A heater H, which may be energized by alternating current, isprovided for each cathode K.

At the upper left of Figure 1 is shown a master oscillator for thecascade, of a well-known regenerative vacuum tube type. As illustratedthe anode-to-cathode circuit of its tube T contains the source of anodepotential +B, resistances R1 and R2 connected in series thereto, and theinductance L1 connected to R2 and to the anode A. Regeneratively coupledto the anode-to-cathode circuit is the grid-to-cathode or frequencycontrol circuit.- In this control circuit a tuned tank impedancecomprising an inductance L2 and a condenser C1 in parallel is connectedbetween the grid G and the cathode K. A small trimmer condenser C2 is inparallel with C1 for critical tuning of the oscillator. The couplingbetween the two circuits is, as shown, between the inductances L1 and L2which have a common ferromagnetic core M as illustrated. Also containedin the grid-to-cathode circuit are a condenser C3 and a resistance R3 inparallel. These serve to provide grid bias for the oscillator and toinsure that it starts oscillating when the system is turned on, bysetting up a transient potential of the grid under initial condition.

Further contained in the grid-to-cathode circuit is a source ofsub-audio alternating voltage (marked Tremolo). This source is employedto provide a frequency tremolo or pitch vibrato in a musical instrumentusing the present oscillation generating system and may take the form ofthe tremolo set forth in the aforementioned. Patent No. 2,230,429. As inthe structure described in the patent the tremolo source (markedTremolo) varies the grid potentials of the present master oscillators,to vary slightly their frequencies and through them the frequencies ofthe members of the attendant cascades, at a sub-audio rate of about 6 C.P. S. to provide the desired pitch vibrato.

As to the main operating characteristics of the master oscillator thetank impedance L2, C1, C2 is tuned to a frequency of 2093 C. P. S.,corresponding to a high C note in the equitempered musical scale basedupon A=440 C. P. 5., through preselections of the values of parts forthe impedance and by vernier setting of the trimmer condenser C2connected therewith. The oscillator thus operates at the desiredfrequency, the oscillations being sustained through the adequatecoupling between its two electrode circuits.

As employed herein the master oscillator is used both to produceoscillations for tone production for the corresponding note and as asource of control pulsations for the attendant cascade of phase-shiftdevices. For deriving oscillations for tone production at the high Cnote of 2093 C. P. S. a series arrangement of a condenser C4, aresistance R4 and a resistance R5 is connected to the anodeto-cathodecircuit of the oscillator, as illustrated one terminal of the condenserC4 being connected to the circuit between the resistance R2 and theinductance L1 and one end of the resistance R5 being connectedto ground;Tone productive 0s cil ati ne arcde i dthroueh h a onnected to thejunction point of the resistances R4. and R5. The oscillations-as thussecured are of com-. pier; character, their waveform being similar tothat shown in Figure 2. For controlling the attendant cascade ofphase-shift devices another lead 2 is employed, connected to theanode-tocathode circuit of the master oscillator at the junction pointof the resistances R1 and R2. The control pulses appearing in this lea2, likewise having the frequency of; 2093 C. P. S., are also of thewaveform shown in Figure 2. The other end of lead 2 is connected to thegrid G of the tube T of the first phase-shift device of the adjoiningcascade, a condenser C5 being interposed in the lead.

I have set forth in the above that phase-shift devicesmay be employed inthis invention either in the oscillatory or non-self-osoillatory state,and that in respect to a musical instrument the use of non-oscillatoryfrequency dividers is particularly advantageous. Consequently in thefollowing I shall describe the devices as being incapableofself-sustained oscillations and the values of parts given thereforwill accordingly relate to this condition. However by appropriate changeof these values the devices can if desired be made self-oscillatory.

Taking up the first phase-shift device of the cascade, adjoiningthemaster oscillatonthe member has an anode-to-cathode circuitcontaining the source of anode potential +B and a resistance Reconnecting thesource and the anode A, and a grid-to-cathode circuitcontaining a phase shifting network comprising the condensers Co and C7and the resistances R7, R3, and, R9. As illustrated the condensers C6and C7 of the network are connected in series, with the condenser C7-oonnected tothe grid G, whereas the resistance R7 is connected tocondenser C6, the resistance R8 is connected to the junction of the twocondensers, and the resistance R9 is connected directly to the grid. Theother ends of the three resistances connect to ground. A coupling lead 3is connected from the anode A to the junction point of condenser C6 andresistance R7 of the network, a condenser Ca being placed in the lead.

The phase-shiftdevice as set forth is incapable of self-sustainedoscillations, being so arranged that under shock from a single externalpulse it will produce a single train of damped oscillations. Thistrainof damped oscillations is illustrated in Figure 3. The frequency ofthe oscillations in the train is arranged to be about 740 C. P. s.(about sixsemitones below the 1046.5 C note) through selections ofvalues for variousparts and by setting the resistance Re which isadjustable as illustrated.

As was above outlined a phase-shift device may be raised in frequency byperiodic pulses of higher frequency so asto operate continuousl as afrequency divider at an exact subharmonic of the pulse frequency. Thusunder the influence of the control pulses at 2093 C; P. S. from themaster oscillator, pulsing the grid G of th first phaseshiftdevice ofthe cascade through the lead 2, the. deviceoperates at an exact octavebelow the master oscillator, i. e., at the 1046.5 C. P. S. C note, andoscillations for tone productive purposes may be derived from the deviceat-that frequency. For this purpose the cathode K is connected to groundthrough a resistance R10, the resistanceRs being grounded through R10,and a tone productive lead I is connected "to-the junction point of thecathode K and the resistance R10.

The waveform of the oscillations derived from the phase-shift device fortone production is illustrated in Figure 4. It will be noted that theseoscillations are of complex character and similar to those derived fromthe master oscillator as shown in Figure 2. It will be further notedthat these oscillations derived from the device when continuouslyoperated by influence of external pulses differ considerably in waveformfrom the damped oscillations of the device when shocked by a singlepulse, the damped oscillations being substantially sinusoidal as shown.I believe that this is caused by cancellation of the lower half of thesinusoidal oscillations by alternate pulses of the incoming series ofcontrolling pulsations.

In a similar manner the first phase-shift device of the cascade controlsthe second so that the latter operates at the 523.25 C. P. S. C note twooctaves below the master oscillator. the second controls the third tothree octaves below the master, and so on throughout the cascade, Figure4 representing the waveform of the tone productive oscillations from.the various members. While I have shown only four dividers in thecascade additional members can be added as indicated by the arrowspointing toward the right from the lowest frequency device illustratedin Figure 1.

As will be noted the various control leads 2 connecting adjacentphase-shift devices of the cascade are each connected from the anode Aof a preceding device to the grid G of a succeeding one. In thisdisclosure various parts have similar functions and values and whereverthis occurs I have'endeavored to denote the parts by similar indicia.Thus the various resistances R7, R3 and R9 are uniform throughout a.cascade with consequent simplicity and economy, the designed.frequencies of the phase-shift devices being arranged through the use ofcondensers of various values in the various phase shifting networks ofthe devices. Accordingly these condensers are indicated by C6 and C7,C10 and C11, C14 and C15, and C18 and C19 for the respective cascademembers. Likewise the condensers interposed in the various leads 2connecting adjacent devices are indicated by C9, C13 and C17, and thecondensers illustrated in the various feedback leads 3 are denoted byC8, C12, C16 and Cat.

In this way oscillations are obtained for tone productive purposes inwhich oscillation waveforms are similar and octave relationships areexact. A remaining problem is to provide substantially in-phaserelationships between octavely related oscillations. I have found inthis regard that if in the cascade system described oscillations arederived from the various members at corresponding points, suchoscillations are substantially out-of-phase, as between the masteroscillator and the first driven member and as between adjacent drivenmembers. However, I obtain the desired result by deriving oscillationsfrom the master oscillator and the first driven member as has alreadybeen described and I. also derive oscillations from the third, fifth,etc. driven members as from the first. As to the second, fourth, etc,driven members, I interpose respective resistances R11 between theirresistances R: and ground and I connect leads I for toneproduction tovthe junction points of these resistances R7 and R11. In this way all theoscillations from a cascade are substantially in phase.

As. aforedescribed; tone productive oscillations are derived from thefirst, third, etc, phaseshift devices across resistances R10 connectedbetween the respective cathodes of these members and ground. Now it willbe noted that the voltage appearing across each of these resistancescomprises not only the oscillation voltage but also a considerable D. C.voltage caused by the average anode-to-cathode current of thecorresponding tube flowing through the resistance, and unless otherwisecounteracted this D. C. voltage produces a loud click in an ensuing tonewhen the corresponding device is connected in playing to the tone colorand reproducing systems of a musical instrument. However I remove thisundesirable eifect by neutralizing this D. C. voltage, by connecting asource of negative potential V to the cathodes of the first, third,etc., phaseshift devices, through respective resistances R12 asillustrated.

In Figure is shown a modified form of phaseshift oscillator havingconsiderable frequency stability. In this modification the phaseshifting network comprises an arrangement of two condensers C21 and C22in series shunted by two resistances R12 and B14 in series, one end ofthis combination, the junction of C22 and R14, being connected to thegrid G of the oscillator tube T and the other end to the feedback lead3. As before the lead 3 is connected to the anode A of the tube, with acondenser C23 interposed in the lead. Shunted between the junction pointof the resistances R12, R14 and ground is a condenser C24, and shuntedbetween the junction point of the condensers C21, C22 and ground is aresistance R15. For deriving tone productive oscillations from thedevice the resistance R15 connects to ground through a resistance R16,the tone productive lead I being connected to the junction of the tworesistances. A resistance R17 is connected from the grid G to ground.The anode-to-cathode circuit contains the source of anode potential +Bconnected to the anode through the resistance Re. For tuning theoscillator to a desired frequency the foregoing parts are preselected invalues, exact frequency being attained through adjustment of a trimmercondenser C25 connected in parallel with the condenser C24.

I have found that the particular modification of a phase-shiftoscillator set forth in Figure 5 has such suificient frequency stabilitythat it may be employed as a master oscillator for a cascade system in amusical instrument. However, I have also found that its stability may besuitably decreased by increasing the value of its resistance R15, to theeffect that the oscillator may be raised in frequency under theinfluence of controlling pulses from a source of oscillations of higherfrequency, so that it operates as a frequency divider at an exactsubharmonic of the frequency of the source. Still further, I have foundby increasing further the value of the resistance R15 that the devicebecomes a non-self-oscillatory frequency divider, to operate similarlyto the dividers of Figure 1.

' I have therefore set forth in Figure 6 two uses of the oscillatormodification of Figure .5. In the left of Figure 6 the device isemployed as a master oscillator, operating at the frequency of the highC note 2093 C. P.'S., whereas in the right of the figure it is employedas non-self-oscillatory frequency divider operating under the control ofthe left member at the 1046.5 C, P. S. C note, as the first member .of adependent cascade. Further members of the cascade are indicated by thearrows pointing toward the right from Figure 6.

A control 1'ead'2 connected from the anode 'A-of the master oscillatorto the grid G of the first driven member, and containing the condenserC26, is illustrated in the figure. The application of a tremolo to themaster oscillator is indicated by the source Tr connected in series withthe resistance R11.

Since'the driven member ofFigure 6 operates at a different frequencyfrom the master oscillator the values for corresponding parts will notnecessarily be the same as in the master oscillator. I have thereforeemployed different indicia in the driven member where different valuesfor corresponding parts are employed; for example the condenser C21 ofthe master oscillator becomes the condenser C22 of the driven member,and-"so on. In particular, the resistance Rl5-0f the master oscillatorbecomes a larger resistance R18 in the driven member.

In Figure '7 the device of Figure 5 is employed as a filter circuit formodifying according to a particular tone color the various oscillationsconducted to it from a keyboard system. I have therefore indicated theelectrical aspects of a keyboard system at the left of Figure 7,including continuations of the leads I through which, as aforedescribed,oscillations are derived from the generating devices of the foregoingfigures. As illustrated in Figure 7 the outer ends of these leads I areconnected to appropriate keyboard operated switches S. These switchespreferably are of gradual contact character such as set forth in UnitedStates Patent No. 2,215,124 issued September 1'7, 1940, to John F.Jordan and myself as joint patentees for Electrical contacts. The otherends of the switches S are connected to an oscillation collector 4,which I have ilustrated by a dashed line to indicate the inclusion ofother connections thereto than those specifically shown. The collector 4terminates in a resistance R19 connected to ground, the tone colordevice of'the' figure being connected to the resistance R19 through alead 5 containing the condenser C31. A lead 6 is also connected to theresistance R19 to indicate the connection of further tone color devicesthereto.

In principle the tone color device of Figure 7 functions similar to aresonating circuit, modifying complex oscillations conducted to it byaltering their harmonic. content within a predetermined frequency. Forthis purpose therefore, the device is arranged to benon-self-oscillatory; consequently it employs the resistance R18,similar to the non-self-oscillatory driven member of Figure 6. As anexample I will arranged the device of Figure 7 to resonate in afrequency band centering approximately at 2000 C. P. 5.; under thisexample its condensers C21 and. C22 therefore correspond to the similarconddensers in the master oscillator of Figure 6 whereas its condenserC32 approximates the mean value of the condenser combination C24, C25 ofthe former. Modified oscillations are derived from the tone color devicethrough a lead 1 connected to the junction point of a condenser andresistancein series between the anode A and ground, the condenser C23being connected to the anode with the resistance. R20 connected toground. This lead 1 contains a switch S which will be similar incharacter to those of the aforementioned Patent No. 2,215,124.

While in the above I have described tubes T each having evacuatedenclosures containing the elements for a single thermionic vacuum tube Iprefer to employ double tubes, so called, in com-- mercial embodimentsof my invention; Such double tubes, each containing the elements for twovacuum tubes, have the advantage of requiring only one half the apparentnumber of tubes which would otherwise be required, thus considerablyreducing the cost and space required. I find that a commercial type ofdouble tube known as a '7F7 is satisfactory for the purpose, and inconjunction with this the following values for other parts in theparticular exemplary embodiments given above, are suitable:

+B=250 volts 06:.002 mfd. V=250 volts 07:.001 mfd. Lz=4 henries C's=.002mfd. L2/L1=6/1 turns ratio 09:.00025 mfd. R1=250,000 ohms 010:.004 mfd.R2=500,000 ohms 011:.002 mfd. Rs=l,000,000 ohms 012:.004 mfd. R4=500,000ohms 013:.0005 mfd. R5=4,000 ohms 614:.008 mfd. Rc=100,000 ohmsC1s=.004= mfd. Rv=50,0(l0 ohms 016:.008 mid. Rs=adjustable Crz=.00l mfd.R9=100,000 ohms 618:.016 mfd. R10=l,500 ohms C19=.008 mid. R11=1,000ohms 020:.016 mfd. R12=5,000 ohms 621 .0005 mfd. R13=200,000 ohms(322:.0005 mfd. R14=200,000 ohms (323 .01 mfd.

R15=50,000 ohms R1s=2,000 ohms R17:2,000,000 ohms C27=.001 mfd.R1a=l00,000 ohms C2a=.001 mfd. R1e=5,000 ohms C29=.002 mfd. R2o=100,000ohms C3n=.002 mfd. C1+C2:.0014'7 mid. C31=.001 mfd. 03:.001 mfd.032:.001 mfd. 04:.002 mfd. 033:.01 mfd.

It will be understood that modifications can be made in my inventionwithout departing from its spirit. Being thus described those featuresof the invention which I consider new and novel and which I desire toprotect by Letters Patent, comprise:

1. An oscillation generating system for an electrical musicalinstrument, comprising a source of stabilized oscillations arranged tooperate at a frequency corresponding to a note in high octave registerof a musical scale, and a series of frequency dividers comprising eachan amplifying vacuum tube containing an anode, a thermionic cathode anda control grid, an anode-tocathode circuit containing a source of anodepotential, a grid-to-cathode circuit containing a phase shifting networkcomprising a combination of capacities and resistances, and a connectionbetween said anode-to-cathode circuit and said network, said dividersbeing arranged successively to resonate below respective suboctavesrelative to said source, a connection between said source and thegrid-to-cathode circuit of the first divider of said series and aconnection between the anocle-to-cathode circuit of each precedingdivider to the grid-to-cathode circuit of the adjacent succeedingdivider, and connections to alternate ones of said dividers for derivingoscillations therefrom in phase with the oscillations in the platecircuits thereof, and connections to the remaining oscillators toderiving oscillations therefrom out of phase with the oscillations inthe plate circuits of the said oscillators, whereby under successiveinfluence originating at said source said dividers operate at successivesuboctaves thereof to provide octavely related oscillations for toneproduction.

2. Apparatus as set forth in claim 1, wherein there is insufficienttransfer of phase-shifted oscillations within said dividers respectivelyto provide completely self-sustained oscillations therein, whereby underinfluence of said source as stated, said dividers operate asnon-self-oscillatory frequency dividers.

3. Apparatus as set forth in claim 1, wherein said connections forderiving oscillations from said dividers comprise connections to saidphase shifting networks in alternate dividers and connections to saidcathodes in the remaining dividers, whereby oscillations as derived fromsaid dividers are substantially in phase.

4. Apparatus as set forth in claim 1, wherein said connections forderiving oscillations from said dividers comprise connections to saidphase shifting networks in alternate dividers and connections to saidcathodes in the remaining dividers, whereby oscillations as derived fromsaid dividers are substantially in phase, and wherein a source ofnegative potential is connected to said cathodes in said remainingdividers to impede the inclusion of direct current shocks inoscillations derived therefrom.

5. Apparatus as set forth in claim 1, wherein said source of stabilizedoscillations consists of a phase-shift oscillator comprising anamplifying vacuum tube containing an anode, a thermionic cathode and acontrol grid, an anode-tocathode circuit containing a source of anodepotential, a gricl-to-cathode circuit containing a phase shiftingnetwork, wherein said network comprises at least two capacitiesconnected in series to said grid and shunted by at least two resistancesin series, a resistance connected between the junction point of saidcapacities and said cathode, and a capacity connected between thejunction point of said resistances and said cathode, and a connectionbetween said anodeto-cathode circuit and said network.

6. Apparatus as set forth in claim 1, wherein said dividers consist eachof a phase-shift device comprising an amplifying vacuum tube containingan anode, a thermionic cathode and a control grid, an anode-to-cathodecircuit containing a source of anode potential, a grid-to-cathodecontaining a phase shifting network, wherein said network comprises atleast two capacities connected in series to said grid and shunted by atleast two resistances in series, a resistance connected between thejunction point of said capacities and said cathode, and a capacityconnected between the junction point of said resistances and aconnection between said anodeto-cathode circuit and said network.

WINSTON E. KOCK.

